Process for refining blister copper



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PROCESS FOR REFINING BLISTER COPPER.

No Drawing. Application May 18, 1954 Serial No. 430,725

3 Claims. (Cl. 75--75)' This invention relates to improvements in the-refining of copper. andmore particularly to the refining. of blister copperto produce flat copper;

As conventionally practiced, the refining'of copperinvolves three major steps, .namely, first, the produotionof copper matte in a reverberatoryfurnace; '-sec'ond,..the treatment of copper matte in'a convertor furnace to produce blister copper; and third, the'further treatment of blister" copper either by fire refining or electrolytic refining to produce a marketable product. The'second step,.wherein the iron and sulphur present in copper matte are oxidized and removed-to leave blister copper as an end product, is'known in'the copper smelting trade as converting.

Converting of copper matte is essentially divided into two parts, the first part being the slagging period during 'which, as air is blown-into themolten'matte, the iron is oxidized and combines with added siliceous flux toform aslag which is'readily removed leaving a molten mass of copper bearing material consisting principallyof copper sulphide. The second part is the finish period during which airis again blown into the molten material, usually at an: elevated temperature of about 2200 F., resulting in the oxidation of the-copper sulphidetoyield metallic copper and sulphur dioxide.

When the copper sulphide has beensubstantiallyxall oxidized the blow is stopped and thelresulting or end product, known-in the:trade as blister copper, is transferred to a fire refinery or electrolytic furnace for further purifying and refining.

In suchfurther purifying and refining treatment, whether by fire refining or electrolytic refining, it is necessary that the blister copper be further. oxidized until at least saturated'with copper oxide, whereupon the blow is usually stopped, the accumulated slag skimmed off, and the copper subsequently reduced and.:cast.-

The process of the present invention departs from present conventional practice in that thefurther purifying and refining of. blister? copper, and; the: saturation thereof with copper oxide, is carried out in the converter in a fraction of the time previously required and without the necessity of transferring the materials to a separate furnace for such further treatment. Moreover, such further treatment may be accomplished at temperatures somewhat lower than those required in the production of blister copper and without the formation of a copper oxide slag, which is harmful to the converter linings.

In practicing the present invention, the refining of copper may be carried out in the conventional manner described above up to and including the production of blister copper in the converter. customarily, the process would be stopped here, the material poured out of the converter and transferred to another furnace for further treatment. However, in accordance with the present invention the blowing of the material is continued beyond the blister stage to and through the worm stage, preferably at a slightly reduced temperature. This further blowing and oxidation of the material is continued until atent the worm isabout to leave the copper, at which time the copperis substantially saturated with copper oxide. At this pointa silica flux of the usual or any' well known type for the purpose is 'addedto the material in the converter and the blow continued; preferably: at a temper-- ature in theneighb'orhood of about 2150 F. until the copper is substantially free of impurities. The-converter is then turned out andxthe blow terminated. The resulting-'productis highlyrefined copper comparable in every-wayto I116 product' obtained by fire refining which, as previously indicated: herein, is conventionally accomplished in a separate: furnace particularlydesigned for the purpose.

The. addition of the silica flux to the r material justaas the worm' is beginning. to-disappear is an important feature of the invention'in ithatait 'causes the granulated slag, formed during such further blowingofl the-"copper past'the blister stage and containing the :principaliimpurities of blister copper, to form a coating, which allows .the copper to be :withdrawn, leaving the impurities in such .coating. Such'coating, moreover, containsilittl'e, if 'any, copper:or"copper oxide, and thenceneedanot' b'e used asa recirculating :load in the. converters.

The particular point at which 'to add the. silica'fiux can be determinedby' taking samplesof the material-as it isblown throughrthe'worm' stage. Thus, as'the blovm'ng iscontinued and successive'samples arestaken, itwill be-noted. that the worm becomessmaller and smaller andv eventually disappears. This is. referred to. in*th'e trade. as blowing 1 the worm 01f theicopper Just? as the worm is-aboutto. disappear, which may'readily' be determined by one skilled'inttheart, theisilicafluxi is added.

An alternative and commercially preferred manner of determining-the proper time. to. add thesilica :fiux is based on observation. of the sparksin theugas stream leaving the converter. Thus, ithas'been" found that when the blowhas progressed to the point where the worm is .just about .to disappear; the. sparks in the gas stream fromthe converter'begin toxappear toibreak 'or burst whereupon the silica =flux'is added :-as before.

Following addition of the flux, the blow iscontinued until .thecopper-is substantiallyfreeiof impurities. The particular time requiredrfo'r 'this' phase of 'thetreatmen-t will depend, of course, on'the size'of'the charge, the blowing'rate, and the exactness with which theJpOinF-Of addition'of the flux was determined. Asan' example, where the charge :is: about to tons of-.the molten mass to which has been'added about-2V2 tonsrof silica or. quartz, flux, the timesrequiredswill'be. approximately iminutes; This may'besvaried;.however,';to suit :the particular conditionsrof treatment; I

The pointat-rwhich ithe blow "lSuiOLbETStOPPed'. and the treatment terminated. may be zdetermined' bylsamplin'g, as before, or alternatively, by observing the characteristics of the gases leaving the converter. Thus, as the blowing is continued, following addition of the flux, it has been found that the gaseous flames leaving the converter become noticeably more transparent until a point is finally reached when the flame becomes almost completely transparent. It is at this point that the copper is substantially free of impurities whereupon the converter should be turned out and the blow terminated.

The silica flux added may be of the type commonly used for the production of blister copper. The amount to be added, will vary, of course, with the particular material and the conditions of treatment. In general, however, it has been found that satisfactory results are obtained if the added flux constitutes from about 2 to about 5 percent, by weight, of the charge.

The temperatures employed in the further refining of blister copper in accordance with the process of the invention need not be higher than those employed in the production of blister copper and will usually be somewhat lower. Thus the temperatures employed at the start of the blow, i.e., after the formation of the blister copper, will generally not exceed about 2250 F. and will usually be somewhat lower as, for example, from about 2150 F. to about 2200 F. As the blow progresses temperatures may be further reduced and it is possible to finish the copper at a temperature as low as about 2050 F.

The process herein disclosed is to be distinguished from a practice sometimes employed in smelters where copper anodes are to be cast as part of the process, namely, the practice of blowing the copper past the blister stage at increased temperatures to oxidize the slag and remove more of the small traces of iron and other impurities remaining in the copper. The gain by doing this is a reduction in the time of lance blowing necessary in the anode furnace itself to remove these impurities. However, due to the high temperatures required, which sometimes run as high as 2600" F., a substantial amount of copper is lost in the slag and thus the slag must be skimmed off and rehandled as a circulating load in the converters. These high temperatures, moreover, quickly burn out the brick linings of the converters making frequent replacements necessary, and finally, the resulting copper must still be blown in the anode furnace for an appreciable time to remove impurities.

In the process of the present invention, on the other hand, the temperatures employed do not exceed those used in the production of blister copper and are'usually somewhat lower. Moreover, the addition of the flux as the worm is about to disappear causes the formation of acoating permitting the copper to be removed and leaving the impurities in the coating.

The process of the present invention represents a complete departure from the conventional methods of refining copper. It makes possible the further refining of blister copper directly in the converter without the necessity of transferring the blister copper to a separate furnace for further treatment. Moreover, such further refining of blister copper is accomplished in a fraction of the time required in conventional practice thereby permitting increased production and more economical production.

As herein used, the term blister copper refers to a product which is essentially free of copper sulphide, and contains 98 percent or more copper by weight, the principal impurities being iron, sulphur, and oxygen. On cooling, blister copper solidifies with a surface covered with craters or blisters. If a section is cut through this copper, it is found to be porous.

The term worm copper, as herein used, refers to a product which contains more copper oxide than blister copper. In other words, it is copper which has been carried further along in the oxidizing process. A sample of worm copper on cooling first solidifies over the top and then the molten copper, under pressure of the contained gases, breaks through the solid layer and runs over it as a worm might crawl. This is commonly spoken of as throwing a worm. As previously indicated herein, if samples are taken of copper as it is blown beyond the worm stage, it is seen that the worm becomes smaller and smaller as the blowing is continued and eventually disappears.

The term flat copper, as herein used, refers to a purified product obtained for example, by the fire refining of blister copper, or by the further refining of blister copper in accordance with the process herein disclosed.

While the process of the invention has been described in some detail the scope of the invention is not to be construed as limited thereby otherwise than as covered in the following claims.

I claim:

1. In the process of refining blister copper in the converter in which it is formed which includes blowing air into a molten mass of blister copper, and continuing the air blow to the worm stage, the improvement comprising refining said blister copper through the worm stage including the steps of adding a silica flux to the mass as the worm is just about to disappear, continuing the blow until the silica flux has formed a solid coating over said mass and pouring said mass out from under said coating.

2. In a process of refining blister copper containing free sulfur in the converter in which it is formed which includes blowing air into a molten mass of blister copper, and continuing the blow until the copper is substantially free of said sulfur, the improvement comprising adding a silica flux to the molten mass of material, and continuing the air blow at a temperature not in excess of about 2150 F. until the silica absorbs said free sulfur and solidifies, and pouring the copper out from under said solidified silica.

3. A process of refining blister copper in the converter in which it is formed which comprises air blowing the same to and through the worm stage at a temperature between about 2050 F. and 2250 F., adding a silica flux to the molten mass of material when the sparks therefrom begin to have the appearance of breaking or bursting, and continuing the air blow until the gaseous flames from the molten mass are substantially completely transparent.

References Cited in the file of this patent UNITED STATES PATENTS 723,500 Thofehrn et a1. Mar. 24, 1903 FOREIGN PATENTS 472,626 Great Britain Sept. 23, 1937 OTHER REFERENCES Newton: Metallurgy of Copper, pages 196, 197, 202, 1942. 

1. IN THE PROCESS OF REFINING BLISTER COPPER IN THE CONVERTER IN WHICH IT IS FORMED WHICH INCLUDES BLOWING AIR INTO A MOLTEN MASS OF BLISTER COPPER, AND CONTINUING THE AIR BLOW TO THE WORM STAGE, THE IMPROVEMENT COMPRISING REFINING SAID BLISTER COPPER THROUGH THE WORM STAGE INCLUDING THE STEPS OF ADDING A SILICA FLUX TO THE MASS AS THE WORM IS JUST ABOUT TO DISAPPEAR, CONTINUING THE BLOW UNTIL THE SILICA FLUX HAS FORMED A SOLID COATING OVER SAID MASS AND POURING SAID MASS OUT FROM UNDERR SAID COATING. 